Ether phospholipids in control and 20∶4-depleted rat PMN: Additional evidence for a 1-0-alkyl-2-20∶4-sn-glycerol-3-phosphocholine specific phospholipase A₂

Abstract

Earlier studies from our laboratory have shown that PAF and LTB₄ biosynthesis are inhibited in rat PMN depleted of its 20∶3 (JBC. '86,261, 7592). To test whether these cells contain sufficient 1-O-alkyl-2-acyl-GPC to support PAF synthesis, phosphotidyl choline was isolated from these 20∶4-depleted cells, fractionated into different subclasses and their fatty acid composition determined. These results were compared with those obtained with control PMN. Both control and 20∶4-depleted PMN contained significantly large amounts of alkylacyl-GPC and diacyl-GPC. Small amounts (4%) of alkenylacyl-GPC were also present. The amount of 20∶3 in 20∶4-depleted cells was more or less equal to the amount of 20∶4 in control cells. About 62% of PC-bond 20∶4 in control PMN and about 56% of PC-bound 20∶3 in the 20∶4-depleted PMN was found associated with the alkylacyl species. These results show that both control and 20∶4 depleted PMN have ample precursor substrates to support PAF biosynthesis and these substrates are enriched with 20∶4 in control cells and with 20∶3 in 20∶4-depleted cells. These findings are consistant with the existance of a highly specific phospholipase A₂ capable of distinguising 20∶4 from 20∶3 containing phospholipids.